The specific aims of this project are to: 1) pharmacologically characterize binding sites for arginine vasopressing (AVP) in the rat brain; 2) to measure the effectiveness of AVP-related peptides to displace 3H-AVP from binding sites in the rat brain; 3) to anatomically locate specific brain regions which possess VP specific binding sites; 4) to study ontogeny and regulation changes of the brain AVP receptor. The rationale for this proposed project stems from evidence that the central nervous system (CNS) may be a target organ for AVP, which has been long known to act peripherall on smooth muscle and kidney epithelia, but whose role as a neuromodulator or neurotransmitter has only recently come to light. Evidence that AVP influences memory, as well as other behaviors, when administered peripherally or intracerebrally, along with anatomic studies showing that extrahypothalamic projections of AVP axons projecting from the magnocellular nuclei to many brain regions strongly suggests that AVP receptors should be distributed in foci throughout the brain. In order to determine whether these regions possess AVP binding sites that might mediate these behavioral and physiological effects of AVP on the CNS, we will use a 3H-AVP which we have successfully used in preliminary studies to localize AVP specific binding sites in rat kidney and several CNS regions. The principal methods will be to incubate frozen, slide-mounted slices of rat brains with 3H-AVP and localize the anatomic sites of binding by autoradiography. Quantitative measures of binding will be done on the brain slices by autoradiographic grain counting and by densitometric image analysis, and by wiping the slices from slides with filter paper and counting radioactivity by scintillation spectroscopy. The location of AVP binding sites will be compared to AVP pathways as determined by immunocytochemistry. Characteristics of binding to anatomically identified regions on the brain slices will be determined with protocols designed to assess specificity of binding, time and temperature dependency, affinity of binding sites for AVP-like peptides, and saturability. To determine the relationship of these specific binding sites to AVP mediated biological and behavioral responses, we will investigate the brain AVP binding system in brains of: 1) Brattleboro rats, which lack AVP; 2) fetal and neonatal. The results of this research will be significant in that they will clarify our understanding of vasopressin's roles in regulation and modification of behavior, and other CNS functions, and could lead to new clinical strategies for the treatment of disorders of these functions.